1. Field of the Invention
This invention relates to a mark-detecting apparatus for detecting marks provided on a recording medium such as a film or a tape.
2. Description of the Prior Art
Heretofore, in an information searching apparatus incorporated in a film reader or the like, use has been made of a film having marks provided at a side edge of the frames of the film and these marks have been optically detected and counted, whereby a desired frame in the film has been automatically searched.
The above-described searching apparatus is designed such that the marks on the film are illuminated by a lamp and the variation in light intercepted by the marks when the film is transported is detected by a mark detector and the output signal of this mark detector is counted by a counter and the count content of this counter is compared with the circuit to a drive control circuit to thereby stop a driving system for transporting the film and bring the desired frame to a standstill at a predetermined position whereat it is projected onto a screen.
However, in the thus constructed searching apparatus, the marks on the film are optically detected by the photoelectric conversion element of the mark detector and therefore, when the quantity of light of the lamp greatly varies (for example, when the lamp has broken and been replaced with a new lamp, or when the lamp has deteriorated, or when the power source voltage has greatly fluctuated), the degree of allowance for the variation in quantity of light for the mark detection is varied and in some cases, the marks cannot be properly detected, and this has given rise to the problem that the wrong frame is searched.
Also, if the concentrations of the base and marks of the film differ variously depending on the kind of the film and the treatment conditions of the film, the marks sometimes cannot be detected properly and, as previously mentioned, this has led to the problem that the wrong frame is searched.